In January 2003 the leading 200 beef industry companies held an unprecedented meeting to develop a "unified battle plan" to eliminate E. coli O157 from their industry using methods based in sound science. This important food-borne pathogen causes >70,000 illnesses yearly in the U.S., >75% of them directly linked to livestock; at present 28% of U.S. cattle carry O157, though they show no symptoms. Preliminary experiments supported by our current NIH/AREA grant suggest that, with targeted research and development, bacteriophages could play a significant role in protecting our food supply. We isolated CEV1, the T4-like phage we have used most, from a flock of sheep found to be highly resistant to gut colonization by O157 during probiotic studies at the Southern Plains USDA/ARS Research Center, our collaborators on this project. We have since isolated promising phages from two other flocks of sheep. The long-term objectives of this proposal are to (1) isolate and characterize further phages capable of infecting E. coli O157:H7, (2) investigate the dynamics and physiology of replication of those phages under conditions relevant to the natural environment and to potential therapeutic applications, i. e. during anaerobic respirative and fermentative growth of the host, and select the most promising phages and multiphage cocktails; and (3) use appropriately-designed mixed-culture fermenters and experiments in sheep to assess the potential for using these phages to reduce the O157:H7 load in the guts of livestock and thus in the foodchain. Such experiments are very well suited to work by our undergraduate students, helping them develop a firm foundation in microbial ecology and physiology, molecular biology, general microbial and anaerobic techniques, and experimental design, along with the satisfaction of contributing significant new research results. In preliminary studies, O157:H7 was successfully eradicated from gut models by CEV1 treatment in 12 days and O157 levels were markedly reduced in sheep in two days by CEV1 and CEV2.